Electronic paper or digital paper, also called e-paper, is an electronic device that is portable and can be opened at any time needed like a paper book, newspaper, or a paper magazine and written on like ordinary paper.
The electronic paper takes the form of an electrophoretic display, which is much advantageous over the conventional flat display in that it can be bent, far lower in production cost and superior in energy efficiency without requiring separate backlight. Such an electronic paper is very definite with a wide viewing angle and capable of providing a memory function that the text does not disappear completely even when the power is switched off.
With these advantages, the electronic paper can be used in a very wide range of applications, such as e-books or self-updating newspapers having a paper-like side and moving illustrations, reusable paper display for mobile phones, disposable TV screen, electronic wallpaper, and so forth, with vast potential for market growth. According to their implementation methods, the electronic papers can be categorized into electrophoretic display, liquid crystal display, toner display (QR-LPD: quick-response liquid powder display), and MEMS (micro-electro mechanical system) display. Among these displays, the electrophoretic display is based on the electrophoretic behavior of charged pigment particles suspended in a dielectric fluid and forms a color or contrast by rearranging charged pigment particles under attraction upon application of a voltage difference between the two opposing electrode panels.
Among the electrophoretic displays, the techniques most approaching commercialization are the microcapsule-based electrophoretic display and the microcup electrophoretic display, both of which use particles as color display elements. The microcapsule-based electrophoretic display is a display device in which a dispersion containing charged particles and a fluid medium is encapsulated into microcapsules and sandwiched between the two opposing electrode panels. The microcup electrophoretic display is a display device in which charged particles or charged particle slurry is enclosed in a concave unit defined by barriers between the two opposing electrode panels.
However, the existing electrophoretic displays can neither provide a wide color range or a high contrast ratio enough to be used in a variety of applications nor guarantee the reactivity to a driving voltage and an ability of adequately sustaining a residual image when the driving voltage is off.